Current high power microwave amplifier applications usually employ travelling wave tubes (TWT) to provide microwave power magnification. However, the drawbacks of TWT amplifiers are significant, such as considerable size and weight. Further, TWT amplifiers require a high voltage driver, such as an electronic power conditioner, that in turn necessitates additional complex accessory circuits and involves high voltage risk. To work linearly, TWT amplifiers are normally backed off from their saturated output power or additional linearization circuits are added, and linearization circuitry usually results in a dramatic increase in the system complexity and cost. In addition, vacuum tubes, including TWT's, typically require operation at a designed output power; however, atmospheric variation may require a source that can change its power level based on conditions in the transmit/receive path. This inevitable variability can often lead to running an amplifier either at too high or too low of a power level for the conditions at hand and can lead to unnecessarily high levels of power consumption. Furthermore, often power amplifiers are required to feed systems that demand continuous operation without substantial interruption, and therefore may require a back-up to be ready and waiting in the event of failure of the primary amplifier. Due to the long warm-up times of vacuum tubes, often an identical tube or power supply needs to be idling in the event of failure of the first tube, further degrading the ability to meet demands for small size, weight, and power efficiency as is often needed for communications satellites, mobile ground stations, radar systems, and other applications especially those supporting mobile, airborne, and space environments.
Alternatively, a solid state power amplifier (SSPA) module for satellite, terrestrial, aerospace, and/or unmanned aerial vehicle (UAV) applications may require compact size and light weight. Further, such applications may require an SSPA module that has more power than one monolithic microwave integrated circuit (MMIC) chip can provide. The SSPA continues to advance into the territory traditionally dominated by the vacuum tube amplifier in terms of increased frequency, power, and bandwidth as the MMIC chips to support them continue to advance, for example with advances in GaN and GaAs semiconductor technology. There are various ways to power combine MMICs into a higher power SSPA assembly. Existing SSPA designs are based on power combiners, such as radial combiners, but they sometimes tend to be bulky, heavy, and/or require complex machining. In an effort to reduce this complexity, such waveguide components are sometimes made in two parts that are assembled, often called a “split block”. Even though split block waveguide structure/combiners can be used to reduce machining complexity, the SSPA may suffer from both leakage problems and joining problems. This problem of building a waveguide from separate parts that must be joined, and general insertion and return loss problems over the bandwidth required, can be compounded or increased by the tolerances and structural accuracy needed to properly guide the propagating waves in a hollow waveguide construction. For example, to minimize the insertion loss and return loss, integration of conductive signal line based waveguides, such as microstrip, CPW (Co-Planar Waveguide), or coax, with hollow waveguides is additionally complicated due to tolerances and alignment that may be required. Because a high power SSPA usually has high loop gain, the RF leakage of a multi-part or traditional combiner system could severely degrade the system performance. In addition, existing SSPA designs may be difficult to manufacture at high frequency, for example at V-band and W-band, and their size and weight may increase the cost of launching a satellite into orbit or make UAV (Unmanned Aerospace Vehicle) applications impossible.
One difficulty faced by previous SSPA designs is that they do not work well at high frequencies. Commonly used components, such as stripline, microstrip line, coax, splitter and combiner structures, all include parasitic effects and may suffer material/substrate loss. Higher frequency signals may be significantly attenuated when passing through these structures. Parasitic effects of interconnections, splitters, combiner structures, and/or the materials used to propagate the signal may contribute to the frequency limitations inherent with the SSPA designs in the art. As frequency increases, the tolerances and accuracy between the electromagnetically critical elements within the passive combining and feed structures become increasingly sensitive to error and so methods of construction that work well at several or several 10's of GHz are unsuitable for obtaining high performance at 40, 60, 90, 180, or 240 GHz.
SSPA designs may include a large number of components that must be manually assembled and tuned after assembly. Many individual pieces of existing SSPA designs require complex machining, such as, for example, extremely high precision milling, wire Electric Discharge Machining (EDM) and/or laser processes which lead to relatively high manufacturing costs and challenges in the part integration and bonding to produce a device with sufficiently good electromagnetic properties, for example, in terms of accumulative insertion and/or return loss. Additionally, in some circumstances, required machining tolerances at high frequencies make mass production difficult because every SSPA may have to be manually assembled and tuned to compensate for the manufacturing tolerances. Accordingly, there may be a need for a solid state high power amplifier module which has more desirable cost, size, precision forming, precision assembly, and/or reliability attributes and that readily lends itself to scalable, and cost-effective, manufacturing methods.